The General Introduction to the Book of Blessings has:
“27 The outward signs of blessing, and particularly the sign of the cross, are in themselves forms of preaching the Gospel and of expressing faith. But to ensure active participation in the celebration and to guard against any danger of superstition, it is ordinarily not permissible to impart the blessing of any article or place merely through a sign of blessing and without either the word of God or any sort of prayer being spoken.”
In the USA edition of the Book of Blessings there is a chapter “Order for the Blessing of Holy Water Outside Mass” which begins at n. 1388. In the original Latin it is n. 1085. It may be used by a Priest or a Deacon. To outline the ceremony:
Introduction – Sign of the Cross by everyone, greeting, introductory words by the celebrant.
Reading, eg John 7:37-39
Prayer of Blessing. There are three of which one is chosen. This is the first:
“Let us pray.
All pray briefly in silence; then, with hands outstretched, the celebrant says the prayer of blessing.
Blessed are you, Lord, all-powerful God,
who in Christ, the living water of salvation,
blessed and transformed us.
Grant that, when we are sprinkled with this water
or make use of it,
we will be refreshed inwardly by the power of the Holy Spirit
and continue to walk in the new life we received at baptism.
We ask this through Christ our Lord.
R.
Amen.”
“1399 After the prayer of blessing, the celebrant sprinkles those present with holy water, as a suitable song is sung; as circumstances suggest, he may first say the following words.
Let this water call to mind our baptism into Christ,
who has redeemed us by his death and resurrection.
R.
Amen.”
The Book of Blessings does not indicate a Sign of the Cross to actually bless the water. But on 14 September 2002 there was a decree that there be the Sign of the Cross by the right hand of the celebrant over the item to be blessed, even if the Book of Blessings does not have this. The Latin original text is at
http://notitiae.ipsissima-verba.org/pdf/aas-2002-684-684.pdf and an unofficial English translation at
Notitiae Responses . So in the above ceremony the Sign of the Cross is made at then end of the Prayer of Blessing.
Sometimes a blessing is made without words. For example with Exposition of the Blessed Sacrament in the monstrance,
Ceremonial of Bishops has in 1109: “the bishop puts incense into the censer and blesses it”. No words are provided for this blessing. But from the context of the ceremony it is fairly clear what is happening.
[Excerpts from the English translation of the
Book of Blessings © 1989, International Commission on English in the Liturgy Corporation. Excerpt from the English translation of
Ceremonial of Bishops © 1989 International Commission on English in the Liturgy Corporation. All rights reserved.]